The prior art is already aware of heat exchangers utilizing corrugated tubes for the heat transfer members which contain and conduct the flow of fluid relative thereto. Examples of heat exchangers with only one corrugated tube incorporated therein are seen in U.S. Pat. Nos. 4,270,601 and 4,437,513.
As mentioned, the present invention utilizes two corrugated tubes disposed on a common axis, and examples of the prior art of that general concept are seen in U.S. Pat. Nos. 2,576,309 and 3,934,618.
In all of the aforementioned examples, the fluids flow separately and independently in each respective tube. In the present invention, the two fluids flow in the required separated paths, but they both flow in contact with each of the corrugated tubes. In fact, one of the fluids flows from the interior of one tube to the exterior of the other tube, and the other fluid flows from the exterior of one tube to the interior of the other tube. In this manner, optimum heat transfer is obtained since there is the desirable function of maximum turbulence in the flow of the fluids through the exchanger, and thus there is maximum contact of the fluids with the walls of the tubes where heat transfer is taking place.
Accordingly, the present invention improves the heat transfer between the fluids, and it also improves the fluid contacting the surface of the transfer material itself which is separating the fluids from each other, and thereby optimum heat transfer efficiency is attained.
Still further, the present invention provides the corrugated type of heat exchanger and wherein there is only minimal opportunity for leakage of the fluids from the exchanger or from one fluid passageway to the other fluid passageway within the exchanger. That is, the heat exchange surfaces themselves are of one continuous tube, and the ends of the tubes are sufficiently sealed with regard to the exchanger headers to thereby minimize the possibilities of fluid leakage within the exchanger.
Still further, the exchanger of the present invention provide for the flow of fluids in an extended path of flow through the exchanger, and that path being a serpentine path so that there is maximum contact of the fluid with the exchanger heat transfer surfaces, at least for a given total length of the exchanger itself. This is accomplished by having the fluid flow in the pattern of the corrugations itself, rather than directly past the corrugations and not into the outer radial extents defined by the corrugations of the heat exchanger tubes.
U.S. Pat. No. 4,204,573 shows a heat exchanger which is simply of a straight tubular construction, rather than corrugated tubes, and it has a flow path which causes the fluids to circulate within the exchanger in a reverse pattern of flow, rather than moving directly through the exchanger. However, that arrangement is not with regard to corrugated tubes which direct the flow between the interior and exterior of the two corrugated tubes and which direct the flow into all regions of the convolutions of the corrugations themselves, as in the present invention.
In the present invention, the fluids may be either liquid or gas, including steam and air, and the two fluids flowing through the exchanger may be in any combination of liquid and gas in their respective two paths and within the confinement of the respective corrugated tubes. Still further, the exchanger of the present invention provides a construction which lends itself to easy and ready disassembly for cleaning, inspection, and the like.
Also, the exchanger of this invention accomplishes the afore mentioned, particularly with regard to presenting optimum serpentine flow and maximum heat exchanger surface area, and does so with a construction which is sturdy and is arranged to withstand internal and external fluid pressures without damage to the tubes or convolutions thereof. That is, the external pressures on the convolutions will not cause the convolutions to distort or further collapse, since the radius at the tips of the convolutions is such that the radial tips structurally support the planar portions intermediate the radial tips and thereby preclude collapse of the convolutions which are subjected to high fluid pressures. Further, for optimum heat exchange efficiency, the flow pattern of the fluid relative to both of the tubes and their respective convolutions is in a cardioid pattern which thereby divides the flow into two directions and thus results in the optimum heat exchange efficiency.